1. Field of the Invention
The present invention relates to a relay welding detector, and more particularly to a relay welding detector for detecting welding of a relay which is disposed between a switching element and a secondary battery in a system for supplying power from the secondary battery to a load through the switching element and which connects or disconnects a power line running from the secondary battery to the load.
2. Description of the Related Art
There has been proposed a relay welding detector and detecting method which detects welding of a relay when operation of an electric motor is started or stopped by operation of a key switch (e.g., Japanese Patent Laid-Open Publication No. Hei 10-144194). In that detector, a terminal voltage of the electric motor is detected in a relay off state immediately before the operation of the electric motor is started by an operator who turns on the key switch, or a state that the operation of the electric motor is stopped and the relay is turned off as the key switch is turned off. It is judged that the relay is welded when the detected terminal voltage exceeds a predetermined value.
However, such welding detectors detect welding only when the electric motor is started or stopped its operation, so that it may need a long time to detect welding after the relay is actually welded. The relay is welded when an unexpected large current flows to the electric motor because of a failure in the system, but if the large current is produced when the electric motor is operating, the operation is continued with the relay in the welded state, and the safety of the system may be adversely affected.
It is an object of the present invention to provide relay welding detector and detecting method which can detect welding of the relay at an earlier stage by increasing a frequency of judgment of the welding of the relay.
In order to achieve the aforesaid object of the present invention, the relay welding detector of the invention is provided with the following manners.
A first relay welding detector according to the present invention may be configured as a relay welding detector for detecting welding of a relay which is disposed between a switching element and a secondary battery in a system for supplying power from the secondary battery to a load through the switching element and which connects or disconnects a power line running from the secondary battery to the load, comprising a recharging and discharging state detector which detects recharging and discharging states of the secondary battery; an interruption instructing device which instructs an interruption of the power line by the relay when it is determined by the recharging and discharging state detector that the secondary battery is not being recharged or discharged when the power line is connected by the relay; and a welding judging device which judges welding of the relay when the interruption is instructed.
In this first relay welding detector of the present invention, when it is determined that the secondary battery is not being recharged or discharged while the power line is connected by the relay, the interruption instructing device instructs interruption of the power line by the relay, and when the interruption is instructed, the welding judging device judges welding of the relay. According to the first relay welding detector of the present invention, when it is determined that the secondary battery is not being recharged or discharged, the relay is interrupted and its welding is judged, even if the power line is connected by the relay, such that welding judgement can be performed more frequently. As a result, welding of the relay can be detected earlier.
In the first relay welding detector of the present invention, the recharging and discharging state detector may be a sensor for detecting an electric current flowing to the secondary battery, and the interruption instructing device is a device for instructing to interrupt the power line by the relay when the detected current has an approximate value 0.
The first relay welding detector of the present invention may comprise a capacitor disposed between the relay and the switching element and a voltage lowering device which lowers the voltage of the capacitor when the interruption instructing device instructs to interrupt the power line by the relay, wherein the welding judging device is a device for judging welding of the relay when the voltage of the capacitor is lowered by the voltage lowering device. Thus, the electric charge stored in the capacitor can be discharged faster, and welding of the relay can be judged more accurately.
In the first relay welding detector of the present invention, the load may be an electric motor which is driven with a three-phase alternating current, the switching element may be an inverter, and the power line may be a line connected to each phase wound around the electric motor.
A second relay welding detector according to the present invention may be configured as a relay welding detector for detecting welding of a relay which is disposed between a secondary battery and an inverter in a vehicle having a drive system for supplying power from the secondary battery to an electric motor through the inverter and which connects or disconnects a power line running from the secondary battery to the electric motor, comprising a running speed detector which detects a running speed of the vehicle; a braking operation detector which detects operation of brakes of the vehicle; an interruption instructing device which instructs interruption of the relay when a running speed detected by the running speed detector is approximately 0 with the power line connected by the relay and operation of brakes is detected by the braking operation detector; and a welding judging device which judges welding of the relay when the interruption is instructed.
In the second relay welding detector of the present invention, when the running speed of the vehicle detected by the running speed detector is approximately 0 with the power line connected by the relay and the operation of brakes is detected by the braking operation detector, the interruption instructing device instructs interruption of the relay, and, when the interruption is instructed, the welding judging device judges the welding of the relay. According to the second relay welding detector of the present invention, when the vehicle has substantially stopped and the brakes are applied, welding of the relay can be judged by instructing disconnection of the power line by the relay even if the power line is connected by the relay. As a result, a frequency of judging the welding of the relay can be increased, and the welding of the relay can be detected earlier.
In the first or second relay welding detector of the present invention, the welding judging device can be a device which is provided with a voltage detector for detecting a voltage between terminals of the relay and judges that the relay is welded when the detected voltage is below a predetermined value. Thus, welding of the relay can be easily detected.
The method for detecting welding of a relay according to the present invention may be configured as a method for detecting welding of a relay which is disposed between a switching element and a secondary battery in a system for supplying power from the secondary battery to a load through the switching element and which connects or disconnects a power line running from the secondary battery to the load, comprising the steps of (a) detecting recharging and discharging states of the secondary battery; (b) instructing an interruption of the power line by the relay when the power line is connected by the relay and it is determined from the detected recharging and discharging states that the recharging and discharging are not being performed; and (c) judging welding of the relay when the interruption is instructed.
In the method for detecting welding of a relay of the present invention, when it is determined that the secondary battery is not being recharged or discharged while the power line is connected by the relay, the interruption of the power line by the relay is instructed, and, when the interruption is instructed, the welding of the relay is judged. According to the method for detecting welding of a relay of the present invention, when it is determined that the secondary battery is not being recharged or discharged, the relay is interrupted and its welding is judged, even if the power line is connected by the relay, such that welding judgment can be performed more frequently. As a result, welding of the relay can be detected earlier.
In the method for detecting welding of a relay of the present invention, the step (a) may be a step for detecting an electric current flowing to the secondary battery, and the step (b) may be a step for instructing interruption of the power line when the detected current value is approximately 0.
The method for detecting welding of a relay of the present invention may further comprise a step (d) for lowering the voltage of a capacitor which is disposed between the relay and the switching element when the step (b) instructs interruption of the power line by the relay, wherein the step (c) may be a step for judging welding of the relay when the voltage of the capacitor is lowered by the step (d). Thus, the electric charge stored in the capacitor can be discharged faster, and welding of the relay can be judged more accurately.
In the method for detecting welding of a relay of the present invention, the step (c) may be a step for judging that the relay is welded when the voltage between the terminals of the relay is below a predetermined value.